One of the most important devices in optoelectronic integrated circuits is the electro-optic (EO) modulator which converts electronic signals into high bit-rate photonic data. Recent years have witnessed breakthroughs in the development of EO modulators.
Unfortunately, the lack of ultrahigh-speed compact EO modulators remains a critical technical bottleneck impeding the wide deployment of the on-chip optical interconnects. Conventional EO modulators have a very large footprint because of the poor electro-optic properties of the current materials used in their manufacture. The use of a high-Q resonator in these modulators might significantly reduce their footprint, but would simultaneously decrease the operation bandwidth and thermal stability which then would require additional components to improve bandwidth and stability. Hybrid semiconductors may partially resolve these issues, but the resulting waveguides in these modulators are still tens to hundreds of micrometers long.
One prior slot waveguide for enhancing and confining light in a nanometer-wide low-index material is illustrated in FIG. 1 and was disclosed in V. R. Almeida, Q. Xu, C. A. Barrios, and M. Lipson, “Guiding and confining light in void nanostructure,” Opt. Lett. 29, 1209 (2004) and in Q. Xu, V. R. Almeida, and M. Lipson, “Experimental demonstration of guiding and confining light in nanometer-size low-refractive-index material,” Opt. Lett. 29, 1626 (2004) which are each hereby incorporated by reference in their entirety. With this waveguide, light enhancement and confinement is caused by large discontinuity of the electric field at high-index-contrast interfaces.
A prior graphene-based surface plasmon modulator is illustrated in FIG. 2 and is disclosed in D. R. Andersen, “Graphene-based long-wave infrared TM surface plasmon modulator,” J. Opt. Soc. Am. B 27, 818-823 (2010) which is hereby incorporated by reference in its entirety. This modulator is proposed for long-wave infrared applications based on electrically switching on/off the surface plasmons on graphene. With this modulator the plasmon losses vary as a function of carrier density, which can be varied by the carrier density with an applied gate bias voltage.
Another prior graphene optical modulator is illustrated in FIG. 3 and is disclosed in M. Liu, X. Yin, E. Ulin-Avila, B. Geng, T. Zentgraf, L. Ju, F.g Wang, and X. Zhang, “A graphene-based broadband optical modulator,” Nature 474, 64 (2011) which is hereby incorporated by reference in its entirety. This broadband EO modulator is based on the interband absorption of graphene. However, compared with the size of on-chip electronic components it is still bulky and more suitable for chip-to-chip optical interconnects. On-chip optical interconnects require EO modulators at the nanoscale. Shrinking the dimensions of existing graphene modulators will result in a very poor modulation depth.